Essentially, not every device using the Internet must have a different IP address from every other device.

In most cases, a user’s device has two layers of IP identification: the IP address that the router (or another DHCP server in a larger network) assigns to the device and the IP address that the Internet service provider (ISP) assigns to the network.

When a user receives data from the Internet, each packet is delivered first to the router or DHCP server, and then the router determines which device inside the network to forward the packet to. In this respect, the router acts like a mail room inside a building; the post office mail carrier delivers the mail to the building’s mail room, and the mail room ensures that each individual piece of mail reaches the correct office. This is a two-level identification method, similar to using both a name and a birth date to identify a specific person.